The present invention relates to an image projection apparatus which projects an image using light from a light source lamp, and more particularly to a cooling structure of the light source lamp.
Image projection apparatuses such as liquid crystal projectors use a discharge light source lamp such as a halogen lamp, a xenon lamp, a metal halide lamp, or an ultra-high pressure mercury lamp.
Such a light source lamp includes a discharge light emitting tube in which its glass tube contains gas including mercury or the like sealed therein and electrodes are formed at the both ends of the glass tube, and a concave mirror (reflector) for converting a light flux from the discharge light emitting tube into a collimated light flux or a converged light flux.
FIG. 7 shows the shape of a common light source lamp 100. A discharge light emitting tube 101 includes a spherical light emitting portion 101A, and a first sealing portion (electrode portion) 101c and a second sealing portion (electrode portion) 101d which respectively extend to a front side and a back side from the light emitting portion 101A. The discharge light emitting tube 101 is connected to a reflector 102 with a connecting member 103.
The light emitting portion 101A and the first sealing portion 101c of the discharge light emitting tube 101 are disposed inside the reflector 102, while the second sealing portion 101d is covered by the connecting member 103 and disposed outside (on the back side) of the reflector 102.
In order to maintain such a light source lamp 100 (discharge light emitting tube 101) in a good discharge light emission state, it is necessary to respectively control the temperatures of an upper portion 101a and a lower portion 101b of the spherical light emitting portion 101A shown in FIG. 7 within ranges of, for example, from 900° C. to 1000° C. and 900±20° C. Temperature control for the sealing portions 101c and 101d is also necessary to maintain them at, for example, not more than 420° C.
Accordingly, most image projection apparatuses have a cooling fan disposed near the light source lamp for forced cooling of the light source lamp using an air guiding member such as a duct.
Japanese Patent Laid-Open No. 2002-174857 discloses an image projection apparatus having a duct structure which divides a cooling air from a cooling fan into a cooling air for cooling the inside of the reflector, a cooling air for cooling the outer circumference of the reflector, and a cooling air for cooling an inner side of an exterior case.
Japanese Patent Laid-Open No. 6-338212 discloses an image projection apparatus capable of cooling various parts of a light source lamp appropriately by dividing, inside a reflector, a cooling air from a cooling fan into a cooling air proceeding toward a light emitting portion of a light emitting tube and a cooling air proceeding toward a sealing portion.
Higher intensity and further noise reduction are desired for image projection apparatuses. Noise from the image projection apparatus is mainly generated in association with cooling of heat generating portions with a cooling fan. Therefore, it is necessary, for noise reduction, to reduce the rotation speed of the cooling fan as much as possible so as to cool various heat generating portions appropriately with a small flow volume of air.
What is desirable about the light source lamp is that cooling airs are guided efficiently to the upper and lower portions of the light emitting portion, and that an appropriate flow volume of a cooling air is also guided toward the sealing portion disposed outside the reflector.
This will be explained in more detail with reference to FIG. 7. The upper portion 101a of the light emitting portion 101A that emits light by a discharge phenomenon is a portion whose temperature becomes the highest in the light emitting tube 101. A too high temperature thereof causes a thermal deformation of the glass tube constituting the light emitting tube 101 or causes an abnormal rise in vapor pressure inside the light emitting tube 101, which may invite a malfunction of the light emitting tube 101.
On the other hand, the lower portion 101b of the light emitting portion 101A has a relatively low temperature in the light emitting portion 101A due to the influence of natural convection of an air therearound. However, lack of appropriate temperature control for the lower portion 101b may reduce lifetime or light emission efficiency of the light emitting tube 101 because it causes abnormality in the cycle of a light emission mechanism.
The sealing portions 101c and 101d seal the gas inside the light emitting tube 101 and are provided with the electrodes. If their temperature becomes too high, a metal material such as molybdenum inside the sealing portions 101c and 101d may oxidize and melt.
Thus, it is important to perform appropriate temperature control for the above-mentioned four portions of the light emitting tube. In contrast, a portion other than the above four portions, for example, a side face 101e of the light emitting portion 101A shown in FIG. 9, hardly affects the performance or lifetime of the light emitting tube even if temperature control by cooling is not performed actively.
However, in the apparatuses disclosed in Japanese Patent Laid-Open Nos. 2002-174857 and 6-338212, the cooling air is guided toward the side face of the light emitting portion 101A as shown in FIG. 8. In other words, the upper portion 101a, the lower portion 101b, and the side face 101e of the light emitting portion 101A shown in FIGS. 7 and 9 are cooled collectively.
That is, in the configurations disclosed in Japanese Patent Laid-Open Nos. 2002-174857 and 6-338212, the cooling of the light emitting tube 101 is not optimized, and more cooling air than necessary is introduced into the reflector 102. This increases the rotation speed of the cooling fan and invites a noise increase associated therewith.